Microtome-blade sharpening machine

ABSTRACT

A machine designed to automatically perform the sharpening of microtome blades in two sequences: roughing, then finishing, without requiring the turning over of the blade. The machine is further characterized by the fact that the blade oscillates vertically in order to bring its edge into alternate contact with two superposed grinding wheels, with the oscillating motion of the blade accompanied by a reciprocal, transverse motion parallel to its cutting edge, and further with an in place, transverse vibrating motion of the blade.

United States Patent [:91

Garin MlCROTOME-BLADE SHARPENING MACHINE [76] Inventor: Maurice Carin, 5rue St. Pirest,

69200 Venissieux, France [22] Filed: Mar. 20, 1973 [2]] App]. No:342,944

[30] Foreign Application Priority Data Mar 32, I972 France 72.1074l [52]U.S. Cl 51/85 BS [5 [1 Int. Cl B24b 3/48 [58] Field of Search 51/85 BS,85 R, 80 BS, 51/8! BS, 86 BS, 80 R, 84 BS, 92 BS, 93, 94 R, 77 R [56]References Cited UNITED STATES PATENTS l,1U2.7l)6 7/l9l4 Winter 5l/85 B5I] 3,895,462 July 22, 1975 l.l88.352 6/l9l6 Odell 5l/85 BS 1,390.7269/l92l Scheiwer 51/77 R 3,589,075 6/l97l Carlson i. 5l/94 R X PrimaryE.raminerDonald G. Kelly Attorney, Agent, or FirmRaymond A. Robic; JErnest Kenney; Arthur Schwartz [57] ABSTRACT 12 Claims, [2 DrawingFigures 31 r r E :1 l; i i F' PATENTEDJUL 22 ms SHEET PATENTEDJUL 22 msSHEET PATENTED L 2 2 SHEET I\IICR()TUME-BLADE SHARPENING MACHINEDES(RIPTI()N OF A PREFERRED EMBODIMENT OF THE INVENTION The presentinvention relates to a machine designed to automatically sharpenmicrotome blades.

The difficulty in perfectly sharpening microtome blades is well known.and is frequently the reason for an excessive number of imperfectcross-sections that are difficult to inspect by practical means.

It is also known that sharpening is an unpleasant. long and tediouswork. which is very frequently left to unskilled or improperly trainedlabor.

Finally. microtome blade sharpening techniques. already treated quitelowly in the mechanical industries. had made little progress withrespect to the precise forming of blade cross-sections useful in thehistological field.

The object of the invention is to automate a microtome blade grindingmachine that incorporates advanced techniques for forming precisecutting angles on the blade.

The machine of this invention is characterized by the fact that itobtains the sharpening of both faces of the blade cutting edge withoutrequiring its turning over. For this purpose. the blade is caused tooscillate vertically so that its edge comes alternatively in contactwith two superposed abrasivefitted sharpening rolls or grinding wheels.This sharpening develops successively in two sequences. one for theroughing and the other for the finishing operation. without changing thevarious adjustments of position. Moreover. another characteristic of themachine consists in the fact that the vertical oscillating motion of theblade is accompanied by an alternating or reciprocating motion oftranslation parallel to the cutting edge of the blade and further by avibratory motion in place in the same general sense as the transversemotion.

In order to obtain these motions ofthe blade. the machine comprises abase. a first lower carriage supporting a second. upper carriage onwhich a blade holder is mounted. and a grinding wheel support andtransfer assembly. By a rectilinear. forward displacement ad justable inamplitude and position. the lower carrier ensures the feeding of theblade in contact with the sharpening rolls and by rcarw ard. retractionat the end of the sequence. withdraws the blades from the sharpeningposition. The upper carrier ensures. b v a displacement perpendicular tothe preceding motion. the aforesaid reciprocating. transverse motion ofthe blade. The blade holder ensures. by a vertical oscillating motionabout a transverse axis. the successive passage of the edge faces incontact with the upper roll. then with the low er roll. The grindingwheel support and transfer assembly ensures. by a 180 rotation of thetransfer means. the successnc prcscntation in working position beforethe blade of the roughing rolls. then of the fin ishing rolls.

Ihe accompanying drawings show. by way of example. but not intended tobe by way of limitation. a prefcrrcd embodiment of the machineconstructed in accordance with the present invention.

FIG. I is a diagrammatic elevation view of the machine of the presentimention:

FIG. 2 is a plan view of FIG. I:

FIG. 3 shows diagrammatically the blade edge positions during rough andfinishing grinding operations;

FIG. 4 is a sectional view of a portion of the grinding wheel drivingsystem and the transfer means;

FIG. 5 is a sectional view taken along line VV of FIG. 4;

FIG. 6 represents the detail of one of the drive pinions for thegrinding wheels;

FIG. 7 shows the detail of the grinding wheel transfer means and aratchet drive assembly for same; and the lower carriage advancing andretracting rack;

FIG. 8 represents a plan view of the upper carriage reciprocating drivesystem and the cam drive assembly for oscillating the blade holder;

FIG. 9 is a front view of the blade holder cam drive assembly. as seenalong line IXIX of FIG. 10;

FIG. 10 is a side view of the blade holder cam drive assembly takenalong XX of FIG. 8;

FIG. 11 is a detailed view of the lower carriage position adjustmentmeans and the blade angle index means; and

FIG. 12 shows operative positions of the lower carriage moving means.

As shown by FIGS. 1 and 2. the machine comprises a base I on which issupported a lower carriage 2 surmounted by an upper carriage 3supporting a blade holder 4. Lower carriage 2 slides as shown by arrowson base I. To the rear of base I are provided supports for a grindingwheel transfer system 7 supporting at least four abrasive-fittedgrinding rolls or wheels; rolls E and E for the roughing operation androlls F and F' for the finishing operation.

The microtome blade is maintained at the end of the blade holder 4 byjaws 8. Blade holder 4 is supported for oscillation about axis 5.

The transfer means 7 may swivel about a transfer shaft 9 by means of alever 60 (FIG. 12] on shaft III. rigid with pinion ll. drivingsimultaneously a rack [2 connected to the lower carriage. and a pinionI3. Pinion [3 is loose on the shaft 9. but rigid with a ratchet drive 14and a ratchet 15 which is biased inwardly by a spring 16 for driving anotched ratchet disc 17 rigidly connected to shaft 9. On the rack 12 isprovided a protrusion [8 designed to release a detent I9 which normallyholds disc l7 fixed. The ratchet l9 pivoted at 20 carries aspring-biased no-back cog 21 biased by spring 22 anchored between theclip 23 and pin 24. The cog 2l is pivotally connected at pin 25 todetent I9.

A grinding wheel drive motor. not shown. at the back of the machine.drives the grinding wheels through a pulley 26 (FIG. 4). which includesa conical pinion 27. The pulley rotates freely with respect to thetransfer shaft 9. This pinion 27 drives a pair of gears 29 mounted onshaft 28 (FIG. 5 each gear having conical and helical gear teeth. Eachhelical pinion drives simultaneously two gears 30 and 3] integral withthe grinding rolls E and F (FIGS. -I and 5).

The peripheral working surfaces of rolls E are separated by a distancebetween centers which is slightly greater than their diameter D in orderto maintain their working surfaces separated. The rolls F have adiameter (I smaller than that of D of the rolls E in order that.according to the FIG. 3. the edge of blade A makes contact with the rollF along a width 1 smaller than the mark I. left by the roll E. Thus. theoperation is rendered very simple. without any particular adjustmentbetween the two operations of roughing and finishing (see FIG. 3).

As shown in FIG. 8. the lower carriage 2 carries a motor. not shownhere. having an output shaft 32 fixed to a crank 33, one end of which iscoupled by a pin 3-4 with a pitman 3S driving the upper carrier 3through a pin or shaft 36. The other end of part 33 comprises a camdrive acting on an elongated cam element 37. Cam 37 is mounted looselyon shaft 38 and includes an eccentric 39 and another elonaged camelement 40 oriented 90 with respect to the cam 37. The cam 40 is movedby contact with abutment 42 fixed on the lower carrier 2 during thereciprocal motion of the upper carrier 3. The axis 38 supports the earns37 and 40 and the eccentric 39 is rigidly fixed with respect to theupper carrier 3 (FIG. 8).

The eccentric 39 causes oscillating vertical motion of a connecting rod41 coupled with a slide block 42 articulating a blade holder dri\elinkage 43 whose end carries a roller 44 by means of pin 45. The roller44 is engaged in a notched member 46 coupled with the carrier 3 by a pin47. The notched member 46 includes a supporting pivot axis 45 traversedby an adjusting screw 49. Member 46 transmits the oscillating motion tothe blade holder 4 pivoted at 50 and permits the adjustment of theposition of the cutting edge of the blade A with respect to a referenceplane X-X' of FIG. I. The blade normally lies in this plane when the cam37 is in the position shown in FIG. 9. The ends of the shaft 45 of theroller 44 are resiliently coupled to the ends of pivot shaft 47 of thenotched member 46 by two springs. not shown here (FIGS. 9 and The bladeholder assembly 4 (FIGS. 1 and 2) includes two laminated springs 51supporting the jaws 8 through a small bar 52 which has adjustment meansto vary the spacing between the jaws.

The rack 12 is fastened to the lower carrier by means of the assembly 53(FIGS. 1 and ll) comprising a threaded shaft 54 and a nut follower 55.The shaft 54 is moved by a central knob 56 provided with an indexpointer 59 movable with respect to a graduated sector 57 showingdirectly the cutting angle of the blade edge.

The operation of the machine is as follows:

After the placing the blade A in the holder in its retracted position.the edge of the blade is adjusted with respect to the reference planeX-X' of FIG. I by means of the control knob 58. and the blade positionis centered in the reference plane.

The rack control lever 60 is brought into the starting reference"position (FIG. 12 intermediate the retracf and *grind positions.

Then. using the control knob 56. the blade A is ad vanced until areference stop means is contacted in the index assembly. and the index59 on the knob 56 is set to the zero position on the graduated scale 57.When the cutting angle is chosen. the knob 56 is adjusted to back thelower carrier 2 rearwardly a distance which corresponds to thewithdrawal of blade A that is neces sary to obtain this chosen angle.these angle values being indicated on the sector 57.

The lever 60 is then rotated fully to the grind position. without anyeffect on the rotation of the transfer means 7, since the protrusion18(FlG. 7) passes under the dctcnt 29 which retracts through its springmeans while the ratchet element on the notched disc 17 continues itsreverse travel opposite to that by which transfer of the grinding wheelsis accomplished (counterclockwise in FIG. 7).

In order to obtain the sharpening time corresponding to the workrequired by the condition of the blade A. a mechanical or electricaltimer (not shown) may he provided.

The starting of the motors of the machine causes the simultaneousrotation of the sharpening rolls EE' and F-F'; the reciprocating motionof the upper carrier 3 (through pitman 35) driving the oscillation ofthe blade holder 4 and the starting of the motor (not shown)transmitting by the intermediary of the laminate springs 51 thetransverse vibratory motion of the blade A.

When the rough grinding or sharpening time has elapsed. the motors cometo a standstill. To inspect the blade A. the crank is reset to startingreference position. If the rough sharpening is satisfactory. the returnrotation of the lever 60 is continued till it reaches the retractposition which is diametrically opposite to the grind position; thisrotation of lever 60 has the effect of rotating transfer means 7 180 andthe presentation of the second rolls FF' in the working position.

For the finish grinding operation. the blade is reset in the same manneras recited above. and lever 60 is returned to the grind position.

The function of the notched member 46 is not only to transmit theoscillating vertical motion of the blade A. but also to operate as aforce limiter for the blade A against the rolls EF. For this purpose.the element 46 comprises two sloped surfaces forming between themselvesan angle of at least against which the roller 44 bears. the said rollerbeing biased into the notch by springs (not shown. for clarity Thevarious working mechanisms are covered by a safety protectingtransparent bonnet. The lifting of the bonnet normally causes thecomplete standstill of the running elements. whilst the closing ofsaidbonnet cannot alone ensure the starting.

Moreover. it is preferred to locate the blade A in a precise manner inrelation to the vertical plane joining the axes of roll pairs EE' andF-F'. by means of a precise detent or stop means 61 on the indexingassembly of FIG. 12 to control the stroke between the startingreference" point and the grind" point to provide for a displacement ofconstant length of the lower carriage 2 when the lever is moved betweenthese positions.

What is claimed is:

1. in a microtome blade grinding machine including means for moving ablade to be sharpened between an advanced sharpening position between apair of driven grinding wheels and a retracted position away from saidgrinding wheels. the improvement comprising:

a. two pairs of grinding wheels mounted for rotation as a unit about atransfer axis. said grinding wheel pairs comprising roughing andfinishing grinders:

h. each of said grinding wheel pairs including spaced grinding wheelsmounted for rotation about paral lel. coplanar axes. one of said pairsof grinding wheels normally being in working position for sharpening ablade edge;

. means for selectively causing said grinding wheel pairs to exchangepositions by rotation of said grinding wheel pairs as a unit about saidtransfer axis; and

. said grinding wheel position changing means being connected to saidblade moving means in such a manner that retraction motion of said bladecauses simultaneous. automatic exchange of position of said grindingwheel pairs.

2. A microtome blade sharpening machine comprising:

a. means for supporting a blade to be sharpened for vertical.oscillating motion with respect to a generally horizontal referenceplane. and about a transverse axis lying in said reference plane: andmeans for oscillating said blade about said axis during a sharpeningoperation.

b. first and second pairs of grinding wheels. each pair being mountedfor rotation about vertically spaced. generally horizontal. transverseaxes. and both pairs being mounted for rotation as a unit about atransfer axis;

. means for driving said grinding wheels about their respective axes:

d. means for advancing said blade to a sharpening position between saidfirst pair of grinding wheels whereby opposite sides of its edge ispresented to each grinding wheel for sharpening when said blade isoscillated;

e. means for retracting said blade to a rearward position away from saidfirst pair of grinding wheels; f. means operable synchronously with saidblade rctracting means for rotating said grinder wheel pairs as a unitabout said transfer axis so as to cause exchange of positions betweensaid grinding wheel pairs. whereby the second grinding wheel pair isplaced in a working position with respect to a blade to be sharpenedwhile said blade is moved to its retracted position;

. the peripheral surfaces of each of said grinding wheel pairs beingnormally separated during a sharpening operation.

3. The microtome blade sharpening machine recited in claim 2 whereinsaid first grinding wheel pair is a roughing grinder and said secondgrinding wheel pair is a finishing grinder.

4. The microtome blade sharpening machine recited in claim 2. furtherincluding means for supporting said blade to be sharpened forreciprocating. transverse motion. and means synchronously operable withsaid blade oscillating means for causing said blade to reciprocatetransversely during a sharpening operation during the time the edge ofsaid blade to be sharpened is in contact with each of said grindingwheels.

5. The microtome blade sharpening machine recited in claim 4. furtherincluding means for vibrating said blade transversely in the same senseas said transverse motion during a sharpening operation.

6. A microtome blade sharpening machine comprising:

a. a base;

b. a lower carriage mounted on said base. said lower carriage movablebetween a forward working position and a rearward retracted position:

c. an upper carriage mounted on said lower carriage for reciprocating.transverse movement. and movable with said lower carriage between theforward and rearward positions of the latter;

d. a blade holder mounted on said upper carriage for movement therewith;

c. means for oscillating said blade holder to cause upward and downwardoscillation of a blade supported in said holder with respect to agenerally hori/ontal reference plane about a transverse. horilontal axisin said plane:

(ill

f. at least a first pair. of grinding wheels supported on said base forrotation about vertically spaced. upper and lower transverse. horizontalaxes. and drive means for rotating said grinding wheels. the peripheralworking surfaces of said grinding wheels being normally separated duringa grinding operation;

g. means for moving said lower carriage between its forward and rearwardpositions. the said forward position placing a blade to be sharpened inworking relationship with respect to said grinding wheels;

b. said blade holder oscillating means causing alternate contact betweenopposite sides of the edge of a blade to be sharpened and each of saidgrinding wheels at least when said lower carriage is at its forwardworking position;

i. means for moving said upper carriage reciprocally transversely atleast while said lower carriage is in its working position andsynchronously with said blade holder oscillating means; whereby saidblade to be sharpened is caused to be advanced to a grinding positionbetween the grinding wheels and oscillated into alternate contact witheach of the grinding wheels while reciprocating transversely during suchcontact;

j. a second pair of grinding wheels also supported for rotation abouthorizontal. transverse. vertically spaced axes. said grinding wheelpairs both being supported for rotation as a unit about a transfer axisfor alternately enabling each pair of grinding wheels to assume aworking position with respect to a blade edge to be sharpened;

k. means operable synchronously with said lower carriage moving meansfor causing said grinding wheel pairs to exchange positions as saidlower carriage is retracted towards its rearward position.

l. each pair of grinding wheels comprising respectively a roughing andfinishing grinder. whereby rough grinding and finish grinding operationscan be automatically performed sequentially on a blade to be sharpened.without requiring removal of the blade from the machine by simply fullyretracting the lower carriage away from the working position andthereafter advancing the carriage forwardly to the working position.

7. The microtome blade sharpener recited in claim 6. further whereinsaid lower carriage moving means includes a rack and pinion assembly.the rack being attached to the lower carriage; a grinding wheel transfermeans. said transfer means including a ratchet drive as sembly actuatedby said pinion, whereby retraction mo tion of said rack caused byrotation of said pinion causes a [80 rotation of said grinding wheeltransfer means about said transfer axis through said ratchet drive. andadvancing motion of said rack does not cause motion of said transfermeans.

8. The microtome blade sharpening means recited in claim 6. furtherincluding a detent locking means for said grinding wheel transfer meanswhereby said transfer means is locked against undesired motion. andmeans cooperating with said rack for releasing said detent when saidrack is retracted a predetermined dis tance. the said ratchet driveassembly permitting lost motion of said pinion. rack. and portions ofsaid ratchet drive assembly to enable said rack to be retracted to anintermediate position without causing motion of said grinding wheeltransfer means.

9. The microtome blade sharpening machine recited in claim 8. furtherincluding a blade sharpening index means said index means comprising anadjustable means for causing relative motion between said lower carrierand said rack. whereby the advanced position of a blade edge to besharpened can be adjusted with respect to the grinding wheels; saidadjustable means being operable separately from said means for advancingand retracting said lower carrier.

10. The microtome blade sharpening machine recited in claim 6, whereinsaid means for reciprocally moving said upper carriage transverselycomprises a motor driven crank and pitman assembly. said crank furtherincluding means for cooperating with said means for oscillating saidblade holder. whereby said reciprocal transverse motion and saidoscillating motion is coordinated during a sharpening operation so thata blade edge to be sharpened is moved transversely while it contactseach grinding wheel; and further wherein said means for oscillating saidblade holder Zll (ill

comprises a cam drive assembly operating a blade holder drive linkagewhich includes a roller engaging a notch having sloped surfaces. andmeans for resiliently urging said roller into engagement with said notchto thereby control the maximum force with which a blade edge to besharpened is driven against a grinding wheel during a sharpeningoperation I]. The mierotome blade sharpening machine recited in claimIt). further including means for adjusting the at rest position of saidblade holder with respect to said blade holder cam drive assembly.

12. The microtomc blade sharpening machine recited in claim 6. whereinthe diameters of said roughing grinder wheels is greater than thediameter of said finishing grinder wheels. whereby the blade edge areato be sharpened in contact with the finishing grinder is smaller thanthe edge area in contact with the roughing grinder when the blade to besharpened is at the same advanced working position.

1. In a microtome blade grinding machine including means for moving ablade to be sharpened between an advanced sharpening position between apair of driven grinding wheels and a retracted position away from saidgrinding wheels, the improvement comprising: a. two pairs of grindingwheels mounted for rotation as a unit about a transfer axis, saidgrinding wheel pairs comprising roughing and finishing grinders; b. eachof said grinding wheel pairs including spaced grinding wheels mountedfor rotation about parallel, coplanar axes, one of said pairs ofgrinding wheels normally being in working position for sharpening ablade edge; c. means for selectively causing said grinding wheel pairsto exchange positions by rotation of said grinding wheel pairs as a unitabout said transfer axis; and d. said grinding wheel position changingmeans being connected to said blade moving means in such a manner thatretraction motion of said blade causes simultaneous, automatic exchangeof position of said grinding wheel pairs.
 2. A microtome bladesharpening machine comprising: a. means for supporting a blade to besharpened for vertical, oscillating motion with respect to a generallyhorizontal reference plane, and about a transverse axis lying in saidreference plane; and means for oscillating said blade about said axisduring a sharpening operation; b. first and second pairs of grindingwheels, each pair being mounted for rotation about vertically spaced,generally horizontal, transverse axes, and both pairs being mounted forrotation as a unit about a transfer axis; c. means for driving saidgrinding wheels about their respective axes; d. means for advancing saidblade to a sharpening position between said first pair of grindingwheels whereby opposite sides of its edge is presented to each grindingwheel for sharpening when said blade is oscillated; e. means forretracting said blade to a rearward position away from said first pairof grinding wheels; f. means operable synchronously with said bladeretracting means for rotating said grinder wheel pairs as a unit aboutsaid transfer axis so as to cause exchange of positions between saidgrinding wheel pairs, whereby the second grinding wheel pair is placedin a working position with respect to a blade to be sharpened while saidblade is moved to its retracted position; g. the peripheral surfaces ofeach of said grinding wheel pairs being normally separated during asharpening operation.
 3. The microtome blade sharpening machine recitedin claim 2 wherein said first grinding wheel pair is a roughing grinderand said second grinding wheel pair is a finishing grinder.
 4. Themicrotome blade sharpening machine recited in claim 2, further includingmeans for supporting said blade to be sharpened for reciprocating,transverse motion, and means synchronously operable with said bladeoscillating means for causing said blade to reciprocate transverselyduring a sharpening operation during the time the edge of said blade tobe sharpened is in contact with each of said grinding wheels.
 5. Themicrotome blade sharpening machine recited in claim 4, further includingmeans for vibrating said blade transversely in the same sense as saidtransverse motion during a sharpening operation.
 6. A microtome bladesharpening machine comprising: a. a base; b. a lower carriage mounted onsaid base, said lower carriage movable between a forward workingposition and a rearward retracted position; c. an upper carriage mountedon said lower carriage for reciprocating, transverse movement, andmovable with said lower carriage between the forward and rearwardpositions of the latter; d. a blade holder mounted on said uppercarriage for movement therewith; e. means for oscillating said bladeholder to cause upward and downward oscillation of a blade supported insaid holder with respect to a generally horizontal reference plane abouta transverse, horizontal axis in said plane; f. at least a first pair ofgrinding wheels supported on said base for rotation about verticallyspaced, upper and lower transverse, horizontal axes, and drive means forrotating said grinding wheels, the peripheral working surfaces of saidgrinding wheels being normally separated during a grinding operation; g.means for moving said lower carriage between its forward and rearwardpositions, the said forward position placing a blade to be sharpened inworking relationship with respect to said grinding wheels; h. said bladeholder oscillating means causing alternate contact between oppositesides of the edge of a blade to be sharpened and each of said grindingwheels at least when said lower carriage is at its forward workingposition; i. means for moving said upper carriage reciprocallytransversely at least while said lower carriage is in its workingposition and synchronously with said blade holder oscillating means;whereby said blade to be sharpened is caused to be advanced to agrinding position between the grinding wheels and oscillated intoalternate contact with each of the grinding wheels while reciprocatingtransversely during such contact; j. a second pair of grinding wheelsalso supported for rotation about horizontal, transverse, verticallyspaced axes, said grinding wheel pairs both being supported for rotationas a unit about a transfer axis for alternately enabling each pair ofgrinding wheels to assume a working position with respect to a bladeedge to be sharpened; k. means operable synchronously with said lowercarriage moving means for causing said grinding wheel pairs to exchangepositions as said lower carriage is retracted towards its rearwardposition; l. each pair of grinding wheels comprising respectively aroughing and finishing grinder, whereby rough grinding and finishgrinding operations can be automatically performed sequentially on ablade to be sharpened, without requiring removal of the blade from themachine by simply fully retracting the lower carriage away from theworking position and thereafter advancing the carriage forwardly to theworking position.
 7. The microtome blade sharpener recited in claim 6,further wherein said lower carriage moving means includes a rack andpinion assembly, the rack being attached to the lower carriage; agrindinG wheel transfer means, said transfer means including a ratchetdrive assembly actuated by said pinion, whereby retraction motion ofsaid rack caused by rotation of said pinion causes a 180* rotation ofsaid grinding wheel transfer means about said transfer axis through saidratchet drive; and advancing motion of said rack does not cause motionof said transfer means.
 8. The microtome blade sharpening means recitedin claim 6, further including a detent locking means for said grindingwheel transfer means whereby said transfer means is locked againstundesired motion, and means cooperating with said rack for releasingsaid detent when said rack is retracted a predetermined distance, thesaid ratchet drive assembly permitting lost motion of said pinion, rack,and portions of said ratchet drive assembly to enable said rack to beretracted to an intermediate position without causing motion of saidgrinding wheel transfer means.
 9. The microtome blade sharpening machinerecited in claim 8, further including a blade sharpening index means,said index means comprising an adjustable means for causing relativemotion between said lower carrier and said rack, whereby the advancedposition of a blade edge to be sharpened can be adjusted with respect tothe grinding wheels; said adjustable means being operable separatelyfrom said means for advancing and retracting said lower carrier.
 10. Themicrotome blade sharpening machine recited in claim 6, wherein saidmeans for reciprocally moving said upper carriage transversely comprisesa motor driven crank and pitman assembly, said crank further includingmeans for cooperating with said means for oscillating said blade holder,whereby said reciprocal transverse motion and said oscillating motion iscoordinated during a sharpening operation so that a blade edge to besharpened is moved transversely while it contacts each grinding wheel;and further wherein said means for oscillating said blade holdercomprises a cam drive assembly operating a blade holder drive linkagewhich includes a roller engaging a notch having sloped surfaces, andmeans for resiliently urging said roller into engagement with said notchto thereby control the maximum force with which a blade edge to besharpened is driven against a grinding wheel during a sharpeningoperation.
 11. The microtome blade sharpening machine recited in claim10, further including means for adjusting the at rest position of saidblade holder with respect to said blade holder cam drive assembly. 12.The microtome blade sharpening machine recited in claim 6, wherein thediameters of said roughing grinder wheels is greater than the diameterof said finishing grinder wheels, whereby the blade edge area to besharpened in contact with the finishing grinder is smaller than the edgearea in contact with the roughing grinder when the blade to be sharpenedis at the same advanced working position.